The present invention relates to an exposure method and apparatus therefor, an exposure system and a mask circuit pattern inspection system, which eliminate an influence of interference light generated in an extremely fine circuit pattern formed on a mask, so that an image is formed with a high resolving power on a substrate through a projection lens and exposed and, further, wherein the light source is an excimer laser light source.
In the manufacture of an LSI, a circuit pattern on a mask is exposed and transferred onto a wafer to form a fine circuit pattern on the wafer. However, to cope with the need of high integration of LSI, the circuit pattern transferred onto the wafer tends to be an extremely fine pattern, which constitutes a resolution limit of an imaging optical system.
In view of the foregoing, various techniques have been developed in order to transfer an extremely fine circuit pattern.
For example, there is a method for exposure using X-rays such as SOR (Synchrotron Organized Resonance) light. There is a further method which uses an EB (Electron Beam) exposure machine. Furthermore, there is another method using an excimer laser disclosed in xe2x80x9cExcimer Laser Stepper for Sub-half Micron Lithography, Akikazu Tanimoto, SPIE, Vol. 1088 Optical Laser Microlithography 2 (1989)xe2x80x9d or Japanese Patent Laid-Open No. 57(1982)-198631.
A theoretical analysis of partial coherent imaging is introduced in xe2x80x9cStepper""s Optics (1), (2), (3) and (4)xe2x80x9d (Optical Technical Contact: Vol. 27, No. 12, pp. 762-771, Vol. 28, No. 1, pp. 59-67, Col. 28, No. 2, pp. 108-119, Vol. 28, No. 3, pp. 165-175).
Also, Japanese Patent Unexamined Publication No. 3-27516 describes an example in which a spatial filter is used to improve a resolving power.
Further, a phase shifter method for modifying a mask to improve a resolving power is known from Japanese Patent Publication No. 62(1987)-50811. According to this phase shifter method, light from a neighboring pattern is made to interfere, thereby enhancing the resolving power, which is realized by providing a film (a phase shifter) with phases alternately deviated through Π so that phases of adjacent patterns are inverted. However, the prior art known from the aforementioned Patent Publication No. 62(1987)-50811 has a problem in that an arrangement of the phase shifter is difficult, and the manufacture of a mask provided with the phase shifter is difficult.
An object of the present invention is to provide an exposure method and an apparatus therefor so that an extremely fine white and black circuit pattern formed on a mask can be transferred onto a substrate with a resolving power equal to or higher than a phase shifter, while solving the aforementioned problem noted with respect to the prior art.
It is a further object of the present invention to provide an exposure method and system, and particularly an excimer exposure method and system, in which data of a transferred pattern on a substrate actually transferred by an exposure apparatus can be confirmed through simulation by arithmetic processing.
It is another object of the present invention to provide a mask circuit pattern inspection system in which even in the case where an extremely fine circuit pattern formed on a mask is different from a pattern transferred onto a substrate, the extremely fine circuit pattern formed on the mask can be inspected with high accuracy.
The aforesaid problem can be solved by the present invention which provides an exposure apparatus or exposure method comprising an illuminating arrangement, such as an excimer laser light source, having coherent property to a certain degree, an imager for imaging light in which a mask (including a reticle) illuminated by the illuminating arrangement is imaged onto a wafer, and a shield for shielding at least a part of the O-order diffraction light out of light which transmits through or reflects from the mask.
The present invention further provides an excimer exposure apparatus wherein a spatial filter shields an area corresponding to the NA of the illuminating arrangement.
Furthermore, the present invention provides an excimer exposure apparatus wherein the illuminating arrangement comprises an integrator and a spatial filter.
Moreover, the present invention provides an excimer exposure apparatus wherein the mask has a circuit pattern formed to have a line width which is substantially xc2xd of an imaging resolving power.
The present invention also provides a projection type exposure apparatus and method comprising an illuminating arrangement for substantially uniformly applying ring-like diffused illumination formed from a number of imaginary point sources to a mask in an exposure area, and a reduction projection lens having an optical eye which shields at least a part of the O-order diffraction light or low-order diffraction light out of light which transmits through the mask substantially uniformly diffused and illuminated by the illuminating arrangement and imaging a circuit pattern formed on the mask onto a substrate in the exposure area, wherein the circuit pattern formed on the mask is sequentially exposed on the substrate by step-and-repeat processing.
The present invention further provides an excimer exposure method which includes the steps of illuminating a mask formed with a circuit pattern, shielding at least a part of the O-order diffraction light out of light which transmits through or reflects from the circuit pattern of the illuminated mask, imaging the light by an imager, and transferring the imaged light onto a substrate.
Furthermore, the present invention provides an excimer exposure method wherein the minimum line width of the circuit pattern on the mask is formed by being suited to an imaging resolving power of the imager.
Moreover, the present invention provides an excimer exposure method wherein the mask has a circuit pattern formed to have a line width which is substantially xc2xd of the imaging resolving power.
The present invention further provides an excimer exposure method wherein the circuit pattern on the mask is formed to have a line width which is substantially xc2xd of the imaging resolving power, and in a wide circuit pattern when transferred onto a substrate, a transmission portion on the mask is formed of a line and space having a pitch of substantially xc2xd to ⅓ of the imaging resolving power or a lattice pattern.
The present invention further provides an excimer exposure method which includes the steps of dividing a circuit pattern formed on a mask into a fine pattern portion and a large pattern portion, imaging them by an imager and transferring the same onto a substrate.
The present invention also provides an excimer exposure system including a mask data converter for converting and producing data of a mask from data, and a calculator for applying arithmetic processing based on a transmission function substantially equivalent to an imager for transferring a circuit pattern formed on the mask using excimer laser light with respect to mask data obtained from the mask data converter to calculate data of the transferred pattern onto a substrate.
The present invention additionally provides a mask circuit pattern inspection system including a mask data converter for converting and producing data of a mask from wiring data, a calculator for applying arithmetic processing based on a transmission function substantially equivalent to an imager for transferring a circuit pattern formed on the mask using excimer laser light with respect to mask data obtained from the mask data converter to calculate data of a transferred pattern on a wafer, an inspection device including an illuminating arrangement for illuminating a mask with the excimer light, an imager for imaging light which transmits through or reflects from a mask illuminated by the illuminating arrangement to a detection position, the imager having a transmission function substantially equivalent to that of the first-mentioned imager, and a light receiver for receiving an imaging circuit pattern imaged on the detection position to obtain an image signal, and a comparator for comparing an image signal obtained from the light receiver of the inspection device with data of a transferred pattern on a wafer calculated by the calculator.
In an exposure apparatus using excimer laser light, for example, the contrast of a circuit pattern transferred onto a substrate is degraded because diffraction light cannot be sufficiently taken into an opening (pupil) of the imager. Light is diffracted according to the using waveform and the dimension of the circuit pattern from the circuit pattern on the mask. At that time, in the case where a circuit pattern is extremely fine, a diffraction angle becomes large, and intensity of diffracted light also increases. As the result, light does not enter an opening of the imager (projection lens) used for transfer, which constitutes the cause for degrading the resolving power.
In order to minimize the loss of the diffracted light, it is contemplated that the wavelength is shortened to reduce diffraction components as in an excimer laser stepper or the NA of the imager (projection lens) is increased so as to receive diffraction light as much as possible.
On the other hand, according to the present invention, with a view to a phenomenon in which less components of diffraction light from a circuit pattern on a mask is received into imager (projection lens) whereas all components (O-order diffraction light) not diffracted from the circuit pattern on the mask are received therein, the O-order diffraction light alone in a large amount of light necessary for imaging is received into the imager (projection lens), and less diffraction light components is relatively received into the imager (projection lens). From a viewpoint of this, at least a part of the O-order diffraction light is shielded thereby to relatively improve a balance in quantity of light between the diffraction light emitted out of the imager (projection lens) and the O-order diffraction light and to improve the contrast of an extremely fine circuit pattern formed on the mask to be imaged and transferred onto the substrate through the imager (projection lens), thus realizing the exposure with high resolving power.
Particularly, in the present invention, there are provided an illuminating arrangement for substantially uniformly applying a ring-like diffused illumination formed from a number of imaginary point sources to a mask in an exposure area, and a reduction projection lens having an optical aye which shields at least a part of the O-order diffraction light or low-order diffraction light out of light which transmits through the mask substantially uniformly diffused and illuminated by the illuminating arrangement and imaging a circuit pattern formed on said mask on a substrate in the exposure area. With this structure, an extremely fine circuit pattern formed on the mask is imaged and transferred onto the substrate through the reduced projection lens to improve the contrast, thus realizing an exposure of high resolving power.
It is noted that although the present invention is hereinafter described in relation to use of excimer laser light, the present invention is not limited to a projection type exposure method using excimer laser light.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show for purposes of illustration only, several embodiments in accordance with the present invention.